76 



THE STUDY OF ANIMAL LIFE CHAP. 



ance of the species and give rise to embryos which start 

 new colonies. Then there are long, lank, sensitive mem- 

 bers, also mouthless, which serve as the sense-organs of 



the colony, and are of use 

 in detecting food or danger. 

 When danger threatens, the 

 polyps cower down, and there 

 are left projecting small hard 

 spines, which some regard as 

 a fourth class of individuals 

 starved, abortive members 

 like the thorns on the haw- 

 thorn hedge. In recognising 

 their utility to the colony as 

 a whole we can hardly over- 

 look the fact that their life as 

 individuals is practically nil. 

 They well illustrate the seamy 

 side of division of labour. 



Herbert Spencer and. Ernst 

 Haeckel have expressed very clearly 

 one law of progress among those 

 animals which form colonies. The 

 crude form of a colony is an aggre- 

 gate of similar individuals, the per- 

 fected colony is an integrate in 

 which by division of labour greater 

 harmony of life has resulted, and in 

 which the whole colony is more thoroughly compacted into a unity. 

 Among the Stinging-animals, we find, some precise illustrations of 

 such integrated colonies, especially in the Siphonophora of which 

 the Portuguese Man- of- War (Physalia) is a good example. There 

 is no doubt that these beautiful organisms are colonies of in- 

 dividuals, which in structure are all referable to a " medusoid ' 

 type. But the division of labour is so harmonious, and the co- 

 ordination of the colony is so thorough, that the whole moves and 

 lives as a single organism. It has become an integrate. 



In many sponges part of the surplus material which abundant 

 nutrition affords is utilised in forming buds, and one bud may 

 fuse with another until a large composite body is built up. But it 

 remains in most cases an aggregate rather than an integrate, a 

 large part may be cut off without making any difference, and there 

 is sometimes a lack of harmonious working in the system of water- 

 currents on which the life of the sponge depends. The higher the 



FIG. 21. COLONY OF Hydr ac- 

 tinia echinala. 



a, nutritive individuals ; b, 

 reproductive individuals ; c, 

 abortive spines ; and there are 

 also long mouthless individuals 

 specialised in sensitiveness. 



(From Chambers's Encyclop. ; 

 after Allman.) 



